Flow rate testing is a common practice for subsea equipment involving long and oftentimes small diameter tubes, such as umbilicals and hydraulic flying leads. The testing is used to confirm the continuity of the tubes, and prove the tubes are able to convey the required volume of fluid within a given time period at a certain inlet pressure. Typically the testing setup includes a hydraulic power unit to provide required pressure, a reservoir tank to collect and supply the fluid continuously, one or more flow rate meters to measure flow rate, one or more pressure gauges to monitor pressure, and hoses to connect all the testing components. During the testing, the inlet pressure is set at a constant pressure, and the corresponding flow rate is measured. When the flow rate is lower than the value expected at a certain inlet pressure, it's an indication that one or more obstructions exist in the tube, which could be due to fluid deposits on the tube wall, or tube cross sectional deformation (e.g., kinked tubes or umbilical buckling). However, testing performed as such can only provide the flow rate corresponding to each inlet pressure, and cannot provide details on the obstruction location when the flow rate is lower than the value expected at a certain inlet pressure. Apparatus and methods have been proposed that can be used to perform the flow rate testing and pinpointing the obstruction location(s) when one or more obstructions exist in the tubes.